Avaaz and the Syrian Observatory for Human Rights reported that there had been attacks on civilians in at least five areas of Syria.

In the northeastern city of Deir Ezzor, Avaaz said that security forces had conducted "a wave of arrests" near to an old airport. In Latakia they reported attacks on a Palestinian camp, while heavy machine gun fire was reported in a nearby residential neighbourhood.

In Homs, Avaaz named one person killed on Thursday after security forces opened fire on a protest. The Syrian Observatory for Human Rights said that a man had been killed by a sniper, though it is not known if the two incidents are related. More than 40 people were arrested on the streets of the city, activists said.

Activists also reported that tanks and troop encampments were "poised" in the outskirts of the city, while snipers remained in place on rooftops.

“Fadi” an Avaaz citizen journalist in Homs, said: “Although there are no tanks inside the city, there are tanks on the outskirts and in the rural areas. Army presence in the city is in the form of snipers scattered around on the roofs of tall buildings. We have a lot of photos and videos of them.

“There was an attack yesterday evening in Deir Baalba by the army and security forces, looking for what they say are arms and weapons, but they found nothing.”

In suburbs of the Syrian capital Damascus there reports of new arrests, including that of an activist who was taken into custody from a hospital where he was being treated for injuries received during a protest earlier this month.

Avaaz told The Huffington Post UK on Thursday that the number of civilians killed by regime forces for whom they have names since the start of the crackdown in mid-March is 2,182. They added that the number may be much higher, due to incomplete information.

More than 8,600 people have been detained in the country, Avaaz said.

The latest phase of the crackdown, which began just before Ramadan, has claimed at least 200 lives in the city of Hama alone.

In a report on human rights in Syria, also released Thursday, the United Nations said that "the disproportionate use of force by Syrian military and security forces violates Syrian international human rights obligations."

It added: "Many civilians, including children, have disappeared. Some bodies were returned to their respective families, many of which bore the traces of torture. The fate and whereabouts of hundreds of detainees remain unknown."